Enzymes (WIP)

Eduqas Core concepts alevel bio

What are enzymes

globular proteins and biological catalysts. They are not used up.

Enzyme active sites

Enzymes are specific as they have an active site which is complementary to the shape of the substrate. Depends on the tertiary structure of enzyme.

Metabolism

all the enzyme/ chemical reaction in a cell

Anabolism

the reactions that build up new, more complex molecules from seperate substrates

Catabolism

the reactions that break down more complex molecules into seperate products 

Metabolic Pathways

a series of reactions where the product of one enzyme is the substrate of another one. Can have branches with different routes

Extracellular enzymes

They work outside of the cell eg. digestive enzymes are made in pancreatic cells and then transported out of the cell to digest food in the gut

Intracellular enzymes

work inside the cell. eg. enzymes for aerobic respiration are found in mitochondria

How do enzymes work?

• When a substrate and an active site collide the substare binds to the active site through interactions in the R group making an enzyme-substrate complex

• Bonds in the substrate distort, straining the bonds that would break and increase the chance of them breaking

• This brings new atoms in the substrate closer and new bonds can form

Activation energy required for the reaction decreases once they bond

Lock and key theory

The active site is a fixed shape. The substrate collides with the active site in the correct oritientation.

Induced fit theory and an example.

As the substrate enters the active site forces of attraction are formed which causes the active site to change shape to fit the substrate.

Activation energy graph

What does a graph showing the effects of temperature on enzymes?

What does a graph showing the effects of substrate concentration on enzymes?

What does a graph showing the effects of pH on enzymes?

What does a graph showing the effects of enzyme concentration on enzymes?

How does temperature affect enzymes and denature them?

As temperature increases, kinetic energy increases which measn it is more likely for the substrate and enzyme to collide and with enough energy so there are more enzyme substrate complexes. After the optinum the hydrogen bonds vibrate and break sothe active sites tertiary (and secondary) shape change and denature.

How does pH effect enzymes?

• Small changes can cause reversible changes to the active site.

• When the pH is low there is more H+ ions so the amine groups takes some and becomes positively charged. When the pH is high there are less H+ ions so the OH group deposits some and becomes negative. This changes how the active site is able to bond so the enzyme cannot lower activation energy and the enzyme is denatured/ inactive

Regulatory enzymes

The rate that a substrate is used or a product is made in metabolic pathways can be controlled by regulatory enzymes at each step

Allosteric enzymes

Two types of reversible inhibators?

Non competitive and competitive

Competitive reversible inhibitor

Structurally similar to normals substrates and compete with them for the active site, slowing down rate of reaction

What happens with competitive inhibators if substrate concentration increases?

They are displaced meaning normal enzyme substrate complexes can form

Non-competitive reversible inhibitors?

They react with the enzyme (not at active site) and change the shape of the whole enzyme including the active site, meaning the substrate can no longer bond

Irreversible inhibitors?

bind covalently and permanantly to the enzyme preventing normal enzyme function.